Electric discharge device and electrode therefor



NOV. 28, 1944. JOHNSON 2,363,531

ELECTRIC DISCHARGE DEVICE AND ELECTRODE THEREFOR Filed NOV. 2'7, 194].

Fig. 1.

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3% d. /5 2 E J B 1 Z I p- 2 4 Discharge Cur r-en't 'Amperes Inventor: Lman B. Johnson, by

His Af't'or'neg Patented Nov. 28, 1944 ELECTRIC DISCHARGE DEVICE ANDELECTRODE THEREFOR Lyman B. Johnson, Cleveland Heights, Ohio, as-

signor to General Ele poration of New York Application November 27,1941, Serial No. 420,638 8 Claims. (01. 176122) This invention relatesto electric discharge devices, and is useful in devices producingradiation tor various purposes, such as germicidal and therapeuticultra-violet lamps and tubes, and lamps or tubes used industrially forirradiating or treating various substances and products, or forblueprinting and other photographic purposes, as well as lamps or tubesfor more ordinary iiluminatlon. Speaking in a general way, the inventionaims at improvement of electric discharge devices as regards blackeningoi envelope walls and wastage of electrodes or cathodes, as well as atobviating the necessity oi activating such electrodes with specialelectron-emissive materials. This application is a continuation-in-partof my application Serial No. 381,633, filed March 4, 1941, now U. 8.Patent No. 2,313,646, granted applicable to both the cooperatingelectrodes, since they function as cathode and anode alter nately.

Discharge devices in which a. discharge is passed between electrodes inan ionizable atmosphere have come into wide use in recent years.Generally, these devices have a metal vapor (such as that of mercury) asthe operating atmosphere, and also include an inert auxiliary orstarting gas (such as one of the rare gases) at pressures up to severalmillimeters. Lamps 01' this character are classified in two groups ortypes, according to the pressure of the mercury vapor. In thelow-pressure group, represented for example by the well-known CooperHewitt lamps, the devices operate at a relatively low temperature, andconsequently at ver low pressure. The discharge at such low pressurescharacteristically spreads out into a uniform glow which fills theentire tube. In the high-pressure field, of which U. S. Patent No.2,202,199 to Germer is representative. the lamp is allowed to heatconsiderably, and the pressures may build up to very high values,ranging anywhere from a fraction of an atmosphere to many atmospheres Assuch pressures, the arc is characteristically constricted into a narrowcord. The dividing line between the two types may be taken as thepressure at which the discharge begins to contract: and this is inpractice determined by the size of the envelope and its consequenttemperature during operation. While the division of types is not welldefined, it does occur somewhere between several hundred millimeters andabout one atmosphere.

ctric Company, a cor- One of the chief problems in the design ofdischarge devices 01' either type for a reasonably long useful life hasbeen the construction of electrodes which do not disintegrate underbombardment to which they are necessarily subjected by the currentcarriers in the arc. This bombardment is caused principally by positivegas ions which are accelerated to high velocities by the so-calledcathode fall. Unless preventive measures are taken, such ions attainsuflicient velocity to knock minute particles oi metal or 01' activatingcoating from a cathode. This phenomenon results in a gradualdisintegration and final destruction oi the cathode, as well as ablackening oi' the tube wall upon which the particles collect,

The destructive eflect. upon the cathode is particularly prevalentduring the starting period of the lamp: i. e., the period of time beforethe cathode has attained proper emission temperature, including, in thecase or the high pressure lamp, the time before the heating of the lamphas built up an atmospheric pressure of full operating value. Thedestructive effect of bombardment during starting on an activatedcathode is enhanced by a tendency of the cathode spot or the arc to jumparound on the surface of the cathode, as if in an attempt to find highiyactivated areas. During the starting period, a relatively highpotential-fall exists in the neighborhood oi the cold cathode, so thatthe positive ions that strike the cathode have much more energy. andproduce more sputtering; and as the pressure (even in the high-pressuretype of lamp) is low at this time, there are relatively few gasparticles to be in collision with the sputtered material from thecathode, and thereby reduce the actual net loss of material bysputtering. On the other hand, when the cathode is at proper emissiontemperature, the cathode fall is greatly reduced; and when the gaspressure (in the high pressure case) is at normal operating value, thecathode is blanketed by gas particles which repel sputtered particles01' metal back to the cathode. After starting is over, therefore,positive ions do not so greatly damage the cathode when they strike it.

The destructive and blackening eflect of cathode bombardment has been sogreat that it has hither proved impossible to construct a commerciallysuccessful discharge lamp with bare or unactivated electrodes; for aboutthe only practicable wa to avoid or reduce the deleterious efl'ects orbombardment has been to provide the is, material which when heated emitselectrons much more copiously than does the cathode metal itself-thusreducing the cathode tall and the energy oi. the bombarding positiveions. Examples oi activators are certain metallic oxides, or materialswhich break down to form the oxides when heated, such as barium orstrontium carbonates or hydroxides. In many cases, also, there isconsiderable dimculty in getting the discharge to start betweenelectrodes without activation.

The activation method of obviating destructive cathode bombardment hasvarious disadvantages, however. In the first place, it is necessary toprovide a tough binder to insure that activating oxides shall adhereproperly to the cathode. It is also generally necessary to subject theactivating materials to some sort 01' an activation process before theyare in proper condition for emission. All this adds to the technicaldifficulties and cost 01' manufacture Activating coatings on a cathodetend to flake off during the life of the cathode, which in itself addsto the blackening of the discharge envelope. Furthermore, activatingmaterial from an electrode deposits on the envelope wall over a greatdistance from its ends; and after initially depositing on the walls, ittends to migrate or spread toward the center of the envelope, thusincreasing the obscuration. Moreover, some of the usual activatingmaterials, such as compounds of the alkaline earth metals, have atendency to initiate devitriflcation oi a quartz or glass envelope.

I have discovered a way of keeping down or reducing the deterioration orloss of material of discharge electrodes, and the blackening orobscuration of the associated discharge envelopes, without necessity foractivating material on or in the electrodes, or for the employment ofauxiliary gas of specially high pressure, as referred to in my pendingapplication above identified, and without any real difllculty instarting the discharge. The invention is not only applicable todischarge devices of the type disclosed in my aforementionedapplication, but also to devices employing working substances andpressures other than there referred to.

In accordance with my invention, I have found that wastage of a barerefractory metal electrode and blackening of the associated envelopewall can be reduced or minimized, without necessity for activation, by asuitable temperature of the electrode or its portion from which thedischarge or are takes oil. This temperature must be high enough toassure the requisite emission of electrons to reduce the cathode falland obviate serious sputtering-just what has heretofore been achieved byactivation-yet low enough to prevent undue evaporation of the refractorymetal, which would produce blackening as serious as that fromsputtering. Evaporation of the refractory electrode metal has not been afactor in the operation of activated electrodes, because the profuseelectron emission from activating materials rendered it quite needlessto approach operating temperatures of the metal at which evaporationwould be appreciable. The optimum temperature for my purpose is that atwhich the combined sputtering and vaporization losses are substantiallyminimized, which for tungsten is substantially oi the order of some2700-3200 K., and even a little lower and higher than this range, at theelectrode area or portion from which the discharge actually takes off.

In the case oi! a "self-heating electrode, the

cathode with so-called activating material-that heat to maintain it orits arcing portion at the desired operating temperature must, of course,come from the action of the discharge or arc. This is practicable, Ifind, ii the electrode body is a part oi limited mass which can beheated rather uniformly, at least in starting, so that enough of itcontributes to the emission oi electrons without any of it ever beingseriously overheated. Accordingly, the electrode body should be fairlycompact and stubby, so that the heat generated where the discharge takesoil may be rather uniformly distributed over a blunt arcing end of saidelectrode body. To assure that the arc shall properly heat theelectrode, taking oi! oi the discharge from the connector, rather thanfrom the electrode body, is prevented. Of course the energy supplied theelectrodes through the lamp leads has to provide all the heat that islost from an electrode arcing end or area whence the discharge takes01!, by conduction and radiation to and from the rest of the electrodeand its current lead and support-as well as the rest of the energyrepresented by the arc or discharge phenomena-so that the heating andthe heat losses balance at the desired operating temperature of saidarea.

In order to prevent or control electrode wastage and envelopeblackening, I not only maintain the electrode (or at least its arcingportion or area where the discharge takes off) at suitable temperatureduring the running of the discharge device, but I provide for heating upthe electrode body or its arcing portion to a suitable operatingtemperature, during starting, before appreciable or serious sputteringcan occur. I have discovered that both rapid heating up and subsequenttemperature maintenance can be assured by artiflcially reducing thethermal conduction of the electric current connector, as by increasingits length beyond what is otherwise needful. When the connector is madeof such limited thermal conduction that in running the heat loss fromthe arcing portion balances the heating thereof from the discharge at anoperating temperature 0 where sputtering losses are kept down withoutincurring serious losses by evaporation of metalor, at the optimum,combined sputtering and vaporization losses are substantiallyminimizedit is found that the electrode (or its arcing portion) willheat up before important sputtering occurs if the electrode is made oflow heat capacity or thermal inertia; in other words, sufilcientlysmall, Conversely, if the electrode is made suillciently small to heatup rapidly, it will also be small enough to be heated sufiicientlyuniformly by the discharge during running.

In a word, then, the mass and thermal capacity of the electrode and thethermal conduction of the connector are correlated, for both startin andrunning, to control the temperature of the electrode and its arcingportion, and the value of the cathode fall. It follows that theelectrode should be designed and proportioned according to the currentin the discharge which it is intended to transmit, and by which it isheated; and any serious deviation from the rated discharge current, inservice, will result in either sputtering or evaporation of electrodemetal, with consequent blackening of the discharge envelope, because ofthe consequent underheating or overheating of the electrode to anoperating temperature outside the above-indicated range.

In order to secure easy starting of the discharge without activation ofthe electrodes, I combine with their other features above set forth aroughened arcing surface. This, I find, greatly reduces the voltagenecessary for starting. Such roughness of the electrode surface mayconsist of grooving formed in a variety of ways, or may reside in thetexture of the refractory metal of the electrode. The rough character ofthe electrode surface is also helpi'ul for assuring that the dischargeshall operate from the electrode body to the virtual exclusion of itsconnector.

During normal running of my device, after a stable condition has beenreached, the pressure of the operating atmosphere of mercury or the likeinfluences electrode wastage and envelope blackening, because it streetsthe temperature of the electrode and its arcing portion or area fromwhich the discharge takes oil. The higher the operating pressure in thelamp, the more constricted is the arc and the smaller the effectivearcing portion or area, and the greater is the heat loss by conductionfrom the electrode to the discharge atmosphere. Moreover, thetemperature of the arcing portion is affected by conduction to the restof the electrode body, which does not attain so high a temperature aswhen the are spreads out over it and so acts to heat it all overdirectly. Hence the electrode temperature is in some measure a functionof the working pressure in the discharge envelope. While smalldifferences in pressure may not be of any great importance, it may bedesirable to take account of very large pressure differences indesigning the electrode.

Pressure of the starting gas is favorable to the suppression ofelectrode wastage and envelope blackening during the starting period ofa discharge device embodying my invention; but it is by no means a majorfactor, as in the lamp set forth in my aforementioned application.

Various features and advantages of the invention besides those alreadyreferred to will appear from the following description of species andforms of embodiment, and from the drawing.

In the drawing, Fig. 1 is a tilted or perspective view of a dischargedevice or lamp embodying my invention, with a wiring diagram of suitableelectric circuit connections; and Figs. 2 and 3 show axial sectionsthrough the ends of this lamp. on a larger scale than Fig. 1.

Figs. 4 and 5 are views generally similar to Figs. 2 and 3 illustratinga somewhat different conformation of the ends of the discharge envelope.

Fig. 6 shows characteristic curves of currentvoltage and arcing tiptemperature for a discharge device embodying my invention.

As shown in Fig. 1 of the drawing, the discharge device a lamp having avitreous elongated or tubular envelope M, of quartz or glass, forexample. provided with solid operating electrodes H, H in its oppositeends, and permeable to ultraviolet and visible radiation. In the presentinstance, there is also a solid auxiliary starting electrode I: in oneend of the envelope l8, closely adjacent the corresponding operating ormain electrode H. A charge of vaporizable and ionizable workingsubstance, such as mercury, is indicated by a droplet l3 inside theenvelope Hi. The charge l3 may either be greater in amount than willvaporize under the heat of the lamp. so that an unvaporized surplus willalways remain, assuring operation of the device with an atmosphere ofsaturated vapor. or the charge l3 may be less than required to affordsuch an unvaporized surplus, so that the lamp will operate with anunsaturated atmosphere. The envelope iii also contains an atmosphere ofstarting gas such as one or more or the rare gases like argon, krypton.xenon, etc. For the device hereinafter described, having the proportionsstated. argon at a pressure or 20 mm. 01' mercury is satisfactory. Theproportions chosen may preferably represent a constriction or theenvelope in such as results in a discharge-constricting pressure thereindurlng normal operation.

bodies H, H are attached. Each inlead II and wtire 2| are joinedtogether by a telescopic joint a 22.

The electrodes Ii, tel-parts of one another) are of relatively small theelectrode H. the electrode H is stubby, so that the Though small intotal mass. shown relatively compact, or

portions behind reaching any very high temperature. A helicalconstruction for the electrode II is here illustrated, and willpresently be described.

electrode H itself. though smaller. This thickness of the connectorassures that the arc will not take 01! from it to the exclusion of theelectrode ii. But while the connector is thus decidedly stout orthick-set as a mere matter of cross-section, this is compensated byextra eifectlve length, so that the actual, eflective heat conduction isrelatively low. To provide this extra length, a loosely coiled helicalform for the connective part II is here illustrated, and will presentlybe described. However, the important point is not any particular meansof securing low heat conduction, but rather the thing for which low heatconduction is the means. Indeed, a fine wire connector without coilingmay be used, if surrounded with suitable insulation to prevent thedischarge from taking oil therefrom.

The low thermal conduction of the connector formed by the connectivepart II and the lead it is determined by two considerations: control ofthe conduction of heat away from the electrode II during running on theone hand, and during starting on the other. During running.

the loss of heat from the arcing portion 20 must balance the heatingthereof by the discharge at an operating temperature for the portion 20at which combined sputtering and vaporization losses are reasonably keptdown or minimized: otherwise, the lamp would blacken badly duringrunning. (In devices with activated electrodes, this condition has notbeen reached, because the ,activation supplied electrons to preventsputtering at temperatures well below that at which vaporization couldbecome serious.) Durin starting, the loss 01' heat from the electrode llmust be so far overbalanced by the heating from the discharge that theelectrode actually heats up to operating temperature before appreciablesputtering can occur.

that engages around the current lead 18 to make atelescopic joint.Actually, the arc may sometimes take on initially from the part 22,especially when a new lamp is started i'or'the very first time. Inaddition to end turns the coiled wire, the electrode Ii may include aheat-distributor in the form of a short wire insert plug 26 fillingthese turns. Preferably this piece 25 is soundly welded to the helicalturns that it occupies, especially the outer end turn, and this turn andthe piece 25 may be ground oi! flush to provide an even end face for thetip 20. The rear socket coils 12 may also be attached by welding to thelead end it around which they fit.

Making the coils forming the electrode II and the connective part IIseparate from the lead it greatly facilitates construction, since itallows of winding wire in a continuous coil whose pitch is suitablyvaried, and simply cutting this coll into sections each consisting ofthe desired turns to form an electrode and connector device.Functionally, however, it will be understood that the coil turns 20, 2!and the straight lead wire it might equally well be one continuouslength of assassi' tially to that in Figs. 1-3, and its correspondingparts and ieaturcs aromafked with the same reference characters.

Illustrative circuit connections for the startin and running or thedischarge device are shown in Fig. i as including ahigh-leakage-reactance transformer T of semi-auto type with its primaryconnected across an A. C. power supply circuit P and with itssecondaries ti, it connected in series across the main dischargeelectrodes II, it. Through a high current-limiting -resistance R and athermal (bimetallic) switch 5, one of the main electrodes ii and theassociated auxiliary starting electrode I! are connected across thetransformer secondaries ti, ti in parallel with the electrodes H, II.The heating resistor r of the thermal switch 8 is shown connected in oneside or the secondary circuit to the main electrodes H, H, so as to beheated whenever the are operates. For a discharge device intended to runon a voltage of 225 volts, the'transiormer '1 may be so chosen as toproduce this voltage across its serially connected secondaries tl, it onopen circuit, and to give a secondary current of about 3.8 amperes onshort-circuit.

Under these conditions, energization of the circuit P will automaticallystart the auxiliary discharge across the short electrode gap II, II andthen the main discharge across the electrode gap II, II. Thereafter thethermal switch 8 will disconnect the auxiliary electrode I! from the secondary circuit, so that the seal around the leads II, I! will not beinjured by the D. C. voltage subsisting between them when both are incircuit: and this switch 8 will remain open at all times when current ison.

For the convenience of those desiring to practice my invention: I willnow give specific conwire, without anything corresponding to the socketturns 22, 21. l

The construction shown in Figs. 4 and d1!- i'ers from that of Figs. 1, 2and 3 in having the molded tube ends Ila, Ila around the electrodes ii,iii smaller than the tube ends, ll, II in Figs. l-3. Otherwise, thisdevice corresponds essenstruction data for lamps such as illustrated inFigs. 1-5 suitable for operation with a discharge current 01' about 3.0amperes, the Figs. 1-3 device being suitable ior an operating voltage ofabout volts and the Figs. 4 and 5 device for about 135 volts. Theselamps may be built with envelope tubes Ill oi clear fused quartz aboutto V4 inch in internal diameter, and with an electrode gap 01' 3 /4inches for the shorter tube of Figs. 1-3, or about 8% inches for thelonger tube oi Figs. 4 and 5. The reduced end chambers i4, ll may eachextend about inch axially of the envelope It, with an internal diameteroi about inch for Figs. 1-3, or inch for Figs. 4 and 5. The inleads l0,l8 and i! may be of 30 mil molybdenum wire, extending into the necks i5,it to about the positions shown,--i e., a distance of about /4 inch i'orFigs. l-3, or 1 inch for Figs. 4 and 5.

The coil forming each electrode ii and its conductor 2| may be 0! 30 miltungsten wire, and may be wound in a lathe on a mandrel wire of the samesize, 1. e., of 0.030 inch diameter. Each coil II, it, 22 may comprisethree close turns Ii 01' per cent pitch (33.3 T. P. 1.), threeloosecoiled, open turns 2| oi 200 per cent pitch (16.7 T. P. 1.), andthree close turns 22 of 100 per cent pitch. In practice, it isadvantageous to wind 8 close turns, 3 open turns, 6 close turns, I openturns, 8 close turns, etc., in alteration. and to cut through the middleof each group of I close turns to form the individual coils or electrodeand connector devices. The heat distributor insert or plug 20 for eachelectrode Ii may consist oi a piece of 30 mil tungsten wire 0.090 inchlong. inserted into the three end turns 20 asoassr and electricallywelded in place in a protective inert or reducing atmosphere. The threeend turns 22 may be similarly welded in place on the inleads IS, IS,before sealing the latter into the glass of the end chambers l5, l5.

For lamps of higher wattages, appropriate enlargement of essential partsmay be found desirable; e. g., a lamp for a discharge current of 6amperes operating at 525 volts may have an envelope ill of 1% inchinternal diameter, an electrode gap of 48 inches, and electrodes ll, llsimilar in essentials to those above described, except that the coils of30-mil wire forming them may be wound on a 45-mil mandrel, their inserts25 may be of this same size, and their inleads l6, l6 may also be ofthis same size.

It will be understood, of course, that the foregoing particulars areillustrative of suitable designs. and are not intended as defining orlimiting my invention in its broader aspects; on the contrary, theproportions and forms of construction can be widely varied.

In operation, the discharge or arc prefers the compact electrode bodyII, with its grooves formed by the close wire convolutions and the plug25 in them, to the connective part 2! where the turns are opened up, orthe socket 22; i. e., even when it starts on the part 22 or on theconnective part 2|, the discharge straightway shifts to the electrode li. As regards the parts ll, 22, this is at once intelligible in view oftheir having about the same mass, since the electrode ii aflords ashorter arc path. It becomes intelligible as regards the parts H, IIwhen it is considered that the openness of the turns :4 makes them amere length of plain, smooth wire. rather than a grooved or otherwiserough-surfaced body like the electrode I I. As already mentioned, thedischarge prefers a rough surface, and starts more easily from such asurface than from a plain, smooth one. Such definite preference of thedischarge for the electrode ii and its tip 26 is important, sinceotherwise the heating effect of the discharge might be so dissipatedover the parts H, 2|, 22, as the are shifted from one part to another,that the electrode ll would not be heated to adequate emissivetemperature, and objectionable sputtering would occur.

While the discharge current is materially highor during the startingperiod than during the stable running condition after the device hasfully heated up-becmuse of the low voltage drop in the discharge underthe low pressure existing in the discharge envelope it at starting-this(1085 not entail material overheating of the electrode II or of its tip20, because under the low pressure during starting the discharge spreadsout over all or most of the surface of the electrode ll, heating itevenly and providing sufflcient electron emission to lower the cathodefall and prevent sputtering during starting. As the mercury pressure inthe envelope HI increases above a value of several hundred millimetersand the device reaches a. stable running condition, however, thedischarge or are contracts to cocupy and heat directly only the endportion or tip 28, including the end turn of the electrode coil and theend of the plug 25, say. (In general. it is the temperature of this endportion that is hereinafter referred to as the operating temperatureduring running.) For example, observations made during normal,stabilized running on an electrode ll constructed and proportioned asillustratively stated above in connection with Figs. 1-5 showed afalling oil of temperature at the starting the lamps can be made 5 rateof about 100 K. to 200 K. per wire turn from the tip Illbacl: to theconnective part 2|. corresponding to a reduction in emission per unit ofarea of as much as per cent in the length of the first electrode turnthat forms the tip 20, so that this first turn aflol'ds by far the majorproportion oi the electron emission from the electrode.

Discharge devices with unactivated solid electrodes afford a variety ofimportant advantages over those with activated electrodes. The electrodeconstruction is simpler and less expensive, special manufacturing stepsincident to activated electrodes are materially shorten The warm-up timein shorter, and changes in the starting voltage during their useful lifedo not occur. There is no active alkaline material of high vaporpressure to be sputtered or vaporized on to the envelope walls, andhence no devitrltlcation or other deterioration of the walls by suchmaterial. 0n the contrary. the only material that can deposit on thewalls by sputtering or vaporization is tungsten or other refractorymetal of the electrodes, which is unreactive toward the vitreousmaterial, deposits only on the very ends of the envelope tube, close tothe electrodes, and does not migrate along the tube toward its middleafter it deposits, as do the ordinary activating materials. Accordingly,the radiant output of the tube is better maintained during its life,both in the luminous range and in. the ultraviolet.

The characteristic of my discharge device with unactivated electrodesdifiers' essentially from that of lamps having activated electrodes;viz., the lamp voltage is dependent on the discharge current, andincreases as the current is reduced. as by a resistor or the like inseries with the lamp. This increase in lamp voltage with reduction incurrent is due to a rapid reduction of the average electrode temperatureand of the thermionic electron emission as the discharge current whichheats the electrode is reduced. Corresponding current-voltage and arcingtip temperature curves for the lamp of Figs. 1-3 are shown in Fig. 6,from which it will be seen that as the discharge current is increased,the discharge voltage approaches an asymptotic minivated electrode,corresponding to the lower emission of electrons from electrode metal ascompared with that from activating materials.

In studying the characteristics of an electrode design, curves such asshown in Fig. 6 should be plotted from a device embodying a pair of theelectrodes and having an unsaturated atmosphere of mercury vapor in therange covered by the curves, in order to obviate masking of theelectrode characteristics by effects arising from condensation andvaporization of mercury.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

I. An electric discharge device of the high-pregsure type comprising aradiation-transmitting envelope containing vaporizable and its exterior,and one of which, ternately as anode and as cathode. is an unactivatedstubby compact refractory metal bodypresentingtofliedischargcaaolidcenteranda blunt arcing end throughoutwhich the high heat from the discharge is distributed by the compactlycmcentrated metal, while the total exposed electrode surface is socorrelated with the rated discharge current through the electrode. andwith the operating pressure of the discharge atmosphere, that theheating of said arcing end by the discharge and the cooling thereof byconduction and radiation to and from the rest of the electrode and itscurrent lead and support are in balance for a temperature of said arcingend that is of the order of 3000" K.

2. An electric discharge device of the high-pressure type comprising aradiation-transmitting envelope containing vaporizable and ionizablemetal and starting gas, together with co-operating widely spacedelectrodes in said envelope which are provided with current leadconnections from its exterior, and at least one of which is acoldstarting, self-heating electrode functioning alternately as anodeand as cathode, and is an unactivated rough, stubby, compact, refractorymetal body presenting to the discharge a solid center and a. bluntarcing end throughout which the high heat from the discharge isdistributed by the compactly concentrated metal, thus producing acorresponding distribution of the discharge over said end, while thetotal exposed electrode surface is so correlated with the rateddischarge current through the electrode, and with the operating pressureof the discharge atmosphere, that the heating of said arcing end by thedischarge and the cooling thereof by conduction and radiation to andfrom the rest of the electrode and its current lead and support are inbalance for a temperature of said arcing end that is of the order of3000 IL, said electrode, fu th more, being of such small total mass andthermal capacity that in starting its said arcing end heats up to atemperature of the order aforesaid before substantial sputtering of therefractory metal can occur; whereby wastage of said electrode andblackening of said envelope wall are prevented or minimized during bothrunning and starting.

3. An electric discharge device of the high-pressure type comprising aradiation-transmitting envelope containing vaporizable and lonizablemetal and starting gas, together with cooperating widely.

spaced electrodes in said envelope which are provided with current leadconnections from its exterior, and at least one of which is a.self-heating electrode functioning alternately as anode and as cathode.and is unactivated and consists of a coil of refractory metal wire anda. refractory metal heat-distributing plug occupying and electricallyand thermally interconnecting the adjacent convolutions of said coil,thus forming a rough, stubby compact body prmenting to the discharge ablunt arcing end throughout which the high heat is distributed by thecompactly concentrated metal, while the total exposed electrode surfaceis so correlated with the rated discharge current through the electrode,and with the operating pressure of the discharge atmosphere, that theheating of said arcing end by the discharge and the cooling thereof byconduction and radiation to and from the rest of the electrode and itscurrent lead and support are in balance for a temperature of said arcingend that is of the order of 3000 K., said electrode, furthermore, beingof such small total mass and thermal capacity that in starting its saidarcing end heats up to a temperature of the order aforesaid beforesubstantial sputtering of the refractory metal can aacasai occur;whereby wastage of said electrode and blackening of said envelope wallare prevented or minimized during both running and starting.

4. An unactivated refractory tungatenelectrode for functionmgalternately as anode and as cathode in a long-gap high-pressuredischarge. said electrode being a stubby compact body presenting to thedischarge a solid center and a blunt arcing end throughout which thehigh heat from the discharge is distributed by the compactlyconcentrated metal, thus producing a corresponding distribution of thedischarge over said end, while the total exposed electrode surface is socorrelated with the rated discharge current through the electrode, andwith the operating pressure of the discharge atmosphere, that theheating of said arcing end by the discharge and the cooling thereof byconduction and radiation to and from the rest of the electrode and itscurrent lead and support are in balance for a temperature of said arcingend that is of the order or 3000" K., said electrode, furthermore,having a rough arcing surface and being of such small total mass andthermal capacity that in starting its said arcing end heats up to atemperature of the order aforesaid before substantial sputtering of therefractory metal can occur.

5. An unactivated refractory metal electrode for functioning in a.long-gap high-pressure discharge, said electrode being a rough, stubbycompact body presenting to the discharge a solid center and a bluntarcing end throughout which the high heat from the discharge isdistributed by the compactly concentrated metal, while the total exposedelectrode surface is so correlated with the rated discharge currentthrough the electrode, and with the energy losses therefrom duringoperation, that the heating of said arcing end by the discharge and thecooling thereof as a result of said energy losses are in balance for atemperature of said arcing end that is of the order of 3000 K.

6. An unactivated refractory metal electrode for self-heating operationin a long-gap highpressure discharge, said electrode being provided witha current connection and consisting of a coil of refractory metal wireand a refractory metal heat-distributing plug occupyin and electricallyand thermally interconnecting the adjacent convolutions of said coll,thus forming a rough, stubby compact body presenting to the discharge ablunt arcing end throughout which the high heat is distributed by thecompactly concentrated metal, while the total exposed electrode surfaceis so correlated with the rated discharge current through the electrode,and with the energy losses therefrom during operation, that the heatingof said arcing end by the discharge andthe cooling thereof'as a resultof said energy losses are in balance for a temperature of said arcingend that is of the order of 3000 K.

7 An unactivated refractory tungsten electrode for functioning in along-gap high-pressure discharge, said electrode consisting of a coil oftungsten wire with a current connection directly thereto, and a tungstenheat-distributing plug occupying and electrically and thermallyinterconnecting the adjacent oonvolutions of said coil, thus forming astubby compact body with a blunt arcing end throughout which the highheat is distributed by the compactly concentrated metal there, while thetotal exposed electrode surface is so correlated with the rateddischarge current through the electrode, and with the operating pressureof the discharge atmosphere, that body, with a current-carrying portionof widely spaced convolutions interconnecting the socket andelectrode-body convolutions, and a refractory metal heat-distributingplug occupy and electrically and thermally interconnecting adjacentelectrode body convolutions of said coil, thus forming a squat, compactbody with a blunt arcing end throughout which the high heat isdistributed by the compactly concentrated metal LYMAN B. JOHNSON.

there.

CERTIFICATE OF CORRECII ON Batent 110.256.5531.

November 28, 191411..

LYMAN B. JOHNSON.

It is hereby certified that error appears in the above numbered patentrequiring correction as follows: In the drawing, strike out Figure 6 inthe lower left-hand corner thereof; and that the said Letters Patentshould be read with this correction therein that the same may conform tothe rec- 0rd of the case in the Patent Office.

Signed and sealed this Zhth day of April, A. D. 19MB.

(Seal) Leslie Frazer Acting Commissioner of Patents.

body, with a current-carrying portion of widely spaced convolutionsinterconnecting the socket and electrode-body convolutions, and arefractory metal heat-distributing plug occupy and electrically andthermally interconnecting adjacent electrode body convolutions of saidcoil, thus forming a squat, compact body with a blunt arcing endthroughout which the high heat is distributed by the compactlyconcentrated metal LYMAN B. JOHNSON.

there.

CERTIFICATE OF CORRECII ON Batent 110.256.5531.

November 28, 191411..

LYMAN B. JOHNSON.

It is hereby certified that error appears in the above numbered patentrequiring correction as follows: In the drawing, strike out Figure 6 inthe lower left-hand corner thereof; and that the said Letters Patentshould be read with this correction therein that the same may conform tothe rec- 0rd of the case in the Patent Office.

Signed and sealed this Zhth day of April, A. D. 19MB.

(Seal) Leslie Frazer Acting Commissioner of Patents.

